A User Equipment (UE) has to feed back Channel Quality Indicator (CQI) information on an uplink channel in a Third Generation Partnership Project (3GPP) Release-8 (Rel-8) Long Term Evolution (LTE) system. A base station (eNB) can perform downlink dynamic scheduling with use of a CQI fed back from the UE. A CQI can be transmitted on a Physical Uplink Control Channel (PUCCH) or a Physical Uplink Shared Channel (PUSCH). In the 3GPP LTE, a Physical Resource Block (PRB) is consisted of twelve Resource Elements (REs) each with a bandwidth of 15 KHz.
FIG. 1 is a schematic diagram of feeding back a CQI on a PUCCH in a 3GPP R8 LTE system. Referring to FIG. 1, each sub-frame is consisted of a series of Orthogonal Frequency Division Multiplexing (OFDM) symbols. Taking a normal CP length as an example, a sub-frame is consisted of two slots each including seven OFDM symbols. CQIs of a plurality of UE are transmitted in each PUCCH OFDM symbol in a CDM mode. Twelve UEs at most can transmit their respective CQIs concurrently in a PRB. Each slot includes two OFDM symbols each as a Reference Signal (RS) and five symbols in which CQI data is transmitted. Each UE can transmit 2-bit channel-encoded CQI data through QPSK in an OFDM data symbol. Therefore in the 3GPP LTE, each UE can transmit 20 encoded CQI data in a sub-frame on a PUCCH. Reference can be made to 3GPP TS36.211, 3GPP TS 36.212 and 3GPP TS 36.213 for details.
In a 3GPP LTE system, a CQI can be transmitted together with data or separately on a PUSCH. FIG. 2 illustrates a schematic diagram of transmitting a CQI separately on a PUSCH in the prior art. Referring to FIG. 2, each slot includes only one Reference Signal (RS) symbol and six data OFDM symbols to transmit the CQI on the PUSCH. 24 encoded CQI bits can be transmitted in each PRB in a QPSK modulation mode in each data OFDM symbol. Therefore in the 3GPP LTE, 288 encoded CQI bits can be carried in a PRB to transmit the CQI separately on the PUSCH. There are typically several tens to hundreds of bits of CQI information on the PUSCH. The transmission of the CQI on the PUSCH is not in a multi-user CDM mode, that is, a CQI of only one user can be transmitted in a PUSCH PRB. Reference can be made to 3GPP TS36.211, 3GPP TS 36.212 and 3GPP TS 36.213 for details.
In a 3GPP LTE-A system, users may have to feed back a larger number of CIQ bits in order to support a more advanced transmission mode. Therefore in the 3GPP LTE-A, the CQI feedback demand can not be accommodated effectively in the Rel-8 PUCCH CQI transmission mode. The use of the Rel-8 PUCCH CQI transmission mode may result in an increased CQI feedback overhead because a PRB can be used for only one UE. In view of 20-bit encoded Rel-8 PUCCH CQI data and 288-bit encoded Rel-8 PUSCH CQI data, it is necessary to devise in the 3GPP LTE-A a new transmission mode in which a CQI is fed back to thereby support effectively a number of sizes of an encoded CQI block while reducing a CQI feedback overhead to the largest extent.